Coated cutting insert with a C porosity substrate having non-stratified surface binder enrichment

ABSTRACT

A cutting insert which comprises a rake face and a flank face wherein there is a cutting edge at the juncture of the rake face and the flank face. The cutting insert has a coating and a substrate wherein the coating is adherently bonded to the substrate. The substrate is a tungsten carbide-based cemented carbide wherein there is a zone of non-stratified cobalt enrichment beginning near and extending inwardly from a peripheral surface of the substrate. The bulk substrate has a porosity of greater than C00 and less than or equal to C04.

BACKGROUND

The invention concerns a coated cemented carbide cutting insert that hasa substrate with a porosity (per the ASTM Designation B 276-86, entitled“Standard Test Method for Apparent Porosity in Cemented Carbides”) ofgreater than C00 and less than or equal to C04 wherein there is a zoneof non-stratified, i.e., generally homogeneous, binder enrichmentbeginning near and extending inwardly from a peripheral surface of thesubstrate.

Heretofore, there has been the Kennametal KC850® coated cutting insert(KC850 is a registered trademark of Kennametal Inc., of Latrobe, Penn.15650, USA, for cutting inserts) which has a C03/C05 porosity substratewhich has a zone of surface binder enrichment. This binder enrichment isa stratified type of binder enrichment meaning that the binderenrichment forms in distinct layers of binder metal. The Nemeth et al.article, “The Microstructural Features and Cutting Performance of theHigh Edge Strength Kennametal Grade KC850,” Proceedings of Tenth PlanseeSeminar, Reutte, Tyrol, Austria, Metalwerke Plansee A.G. (1981), pp.613-627, describes the “Kennametal KC850®” coated cutting tool (orinsert). The “Kennametal KC850®” coated cutting insert has a tri-phasecoating of TiC—TiCN—TiN, according to U.S. Pat. No. 4,035,541, to Smithet al., entitled “Sintered Cemented Carbide Body Coated with ThreeLayers.”

SUMMARY

The invention is a cutting insert which comprises a rake face and aflank face wherein there is a cutting edge at the juncture of the rakeface and the flank face. The cutting insert has a coating and asubstrate wherein the coating is adherently bonded to the substrate. Thesubstrate is a tungsten carbide-based cemented carbide which has a bulkcomposition of between about 3 to about 12 weight percent cobalt, up toabout 12 weight percent tantalum, up to about 6 weight percent niobium,up to about 10 weight percent titanium, and the balance tungsten andcarbon. There is a zone of non-stratified cobalt enrichment beginningnear and extending inwardly from a peripheral surface of the substrate.The zone of non-stratified enrichment has A porosity. The bulk substratehas a porosity of greater than C00 and less than or equal to C04.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings which form a partof this patent application:

FIG. 1 is an isometric view of a specific embodiment of an SPGN 432style of cutting insert;

FIG. 2 is a cross-sectional view of the cutting insert illustrated inFIG. 1 taken along section line 2—2;

FIG. 3 is an isometric view of a specific embodiment of an SNG 433 styleof cutting insert; and

FIG. 4 is a cross-sectional view of the cutting insert illustrated inFIG. 3 taken along section line 4—4.

DETAILED DESCRIPTION

Referring to the drawing figures, FIG. 1 illustrates a specificembodiment of the present invention as an indexable cutting insertgenerally designated as 10. Cutting insert 10 has cutting edges 12 atthe junction of the rake face 14 with the flank faces 16. Although thecutting insert 10 shown in FIG. 1 is an SPGN 432 style with a honedcutting edge, applicant contemplates that the present invention includesother styles of cutting inserts with or without honed cutting edges.

FIG. 2 shows a cross section at the cutting edge 12 of cutting insert 10taken along section 2—2 of FIG. 1. The substrate generally designated as18 has a non-binder enriched zone 20, i.e., a zone comprising thecentral portion (or bulk region) of the substrate, and an outer (orperipheral) binder enriched zone 22 near the peripheral boundaries 24and 26 of the substrate. The outer binder enriched zone 22 exhibits anon-stratified type of binder enrichment. In other words, the binderenriched zone 22 is generally homogeneous in nature. This is indistinction to a zone of stratified binder enrichment in which thebinder forms as layers one on top of the other such as discussed inKobori et al., entitled “Binder Enriched Layer Formed Near the Surfaceof Cemented Carbide,” Powder and Powder Metallurgy, Vol. 34, No. 3, pp.129-133 (April 1987).

In a preferred embodiment, the substrate 18 is a tungsten carbide basedcemented carbide substrate containing at least 70 weight percenttungsten carbide, and more preferably, at least 80 weight percenttungsten carbide. The binder is preferably cobalt or a cobalt alloy and,preferably, has a bulk concentration of 3 to 12 weight percent. The morepreferable bulk cobalt content is between about 5 to about 8 weightpercent. Even more preferably, the bulk cobalt content is between about5.6 to about 7.5 weight percent.

The substrate 18 also contains solid solution carbide and/orcarbonitride forming elements such as titanium, hafnium, zirconium,niobium, tantalum and vanadium, with these elements being preferablyselected from titanium, niobium and tantalum, either alone or incombination with each other or tungsten. These elements preferably maybe added to the mix as a carbide, nitride and/or carbonitride, and morepreferably as a nitride, and most preferably, as tantalum (niobium)carbide and titanium nitride. Preferably, the concentration of theseelements is within the following ranges: up to 12 weight percenttantalum, up to 10 weight percent titanium, and up to 4 weight percentniobium. More preferably, the sum of the tantalum content and theniobium content is between about 3 and about 7 weight percent and thetitanium content is between about 0.5 and about 5 weight percent. Mostpreferably, the sum of the tantalum content and the niobium content isbetween about 5.0 and about 5.9 weight percent, and the titanium contentis between about 1.7 and about 2.3 weight percent.

In the bulk region 20 of the substrate 18, these elements (i.e.,titanium, hafnium, zirconium, niobium, tantalum and vanadium) form, atleast to some extent and preferably for the most part, solid solutioncarbides and/or solid solution carbonitrides with the tungsten carbidein the substrate. In the enriched zone 22, the solid solution carbidesand/or carbonitrides have been wholly, or partially, depleted so thattungsten carbide and cobalt comprise the majority of the composition ofthe binder enriched zone 22.

Within the binder enriched zone 22, the binder (e.g., cobalt) contentshould reach a maximum value which is between about 125 to about 300percent. A more preferable range of binder enrichment is between about150 and about 300 percent of the bulk binder content. The mostpreferable range of binder enrichment is between about 200 and about 300percent of the bulk cobalt concentration in the substrate.

The binder enriched zone 22 preferably extends to the substrateperipheral surfaces 24 and 26. In the alternative, there may be a thinlayer adjacent to these peripheral boundaries (24, 26) in which cobaltcontent has been reduced due to evaporation during substrate sinteringso that the zone of binder (e.g., cobalt) enrichment 22 extends to nearthe peripheral surface (24, 26) of the substrate 18. The thickness ofthe binder enriched zone is preferably up to about 50 micrometers (μm).

Bonded onto the peripheral boundaries 24 and 26 of the substrate 18 is ahard coating, designated by brackets as 29, preferably having one ormore layers applied by chemical vapor deposition (CVD) or a combinationof CVD and physical vapor deposition (PVD) techniques. MTCVD (mediumtemperature CVD) techniques may be used to apply a layer, such as atitanium carbonitride layer. These layers may comprise a base layer 30,an intermediate layer 32, and an outer layer 34. Although FIG. 2illustrates the layers as having different thicknesses, it should beappreciated that is for illustrative purposes only. The thickness ofeach layer (30, 32, 34) depends upon the specific application for thecutting insert.

The base layer 30 is deposited directly onto the surface (24, 26) of thesubstrate 18. The thickness of the base layer 30 preferably variesbetween about 3 micrometers (μm) and about 6 μm. While the compositionof the base layer can vary, preferred compositions may include, forexample, titanium carbide, titanium carbonitride, and titanium nitride.The intermediate layer 32 is deposited directly onto the surface of thebase layer 30. The thickness of the intermediate layer 32 varies betweenabout 2 μm and about 5 μm. While the compositions of the intermediatelayer(s) can vary, preferred compositions may include titaniumcarbonitride, titanium nitride, titanium carbide, alumina, titaniumaluminum nitride and their combinations. The outer layer 34 is depositeddirectly onto the surface of the intermediate layer 32. The thickness ofthe outer layer 34 varies between about 1.5 μm and about 4 μm. While thecomposition of the outer layer can vary, preferred compositions mayinclude titanium nitride, titanium carbonitride, titanium aluminumnitride, and alumina.

While the above description mentions suitable candidates for the coatinglayers, the preferred coating scheme uses a base coating of titaniumcarbide, an intermediate coating of titanium carbonitride, and an outercoating of titanium nitride.

U.S. Pat. No. 4,035,541, to Smith et al., discloses a three layercoating that is applicable to the cutting insert illustrated in FIG. 2.In addition, the coating scheme may be applied by a combination of CVDand PVD, such as those processes described in U.S. Pat. No. 5,250,367,to Santhanam et al., for a “Binder Enriched CVD and PVD Coated CuttingInsert,” and U.S. Pat. No. 5,266,388, to Santhanam et al., for a “BinderEnriched Coated Cutting Insert.” Applicant hereby incorporates U.S. Pat.No. 4,035,541, to Smith et al., U.S. Pat. No. 5,250,367, to Santhanam etal., and U.S. Pat. No. 5,266,388, to Santhanam et al., by referenceherein.

As shown in FIG. 2, for a cutting insert used in milling applications,it is preferred that the binder enriched zone 22 be present underneathperipheral boundaries which lie parallel to the rake face 14 and flankfaces 16 of the cutting insert 10. In other applications such as, forexample, turning, it is contemplated that the enriched zone would bepresent under only the rake face with the zone of enrichment having beenremoved (e.g., by grinding) from the other faces. In this regard, thecutting insert 40 depicted in FIGS. 3 and 4, which is an SNG 433 styleof cutting insert, presents a microstructure in which the enriched zoneis present only under the rake faces.

Referring to FIGS. 3 and 4, cutting insert 40 has four flank faces 42which intersect with one rake face 44 and another rake face (notillustrated) opposite from the one rake face 44 so as to form eightcutting edges 48. Cutting insert 40 has a substrate generally designatedas 49 with peripheral boundary 52 at the rake face and a peripheralboundary 54 at the flank face. The substrate 49 has a bulk portion 50which comprises the majority of the substrate 49, and a layer of binderenrichment 56 near the peripheral boundary 52 at the rake face. Binderenrichment is absent from the bulk portion 49 including the volume nearthe peripheral boundary 54.

The substrate 49 for cutting insert 40 is of essentially the samecomposition as that for cutting insert 10. The levels of binderenrichment are also essentially the same for cutting insert 40 as thosefor cutting insert 10. The basic coating scheme (shown in brackets as59) is also essentially the same for cutting insert 40 as for cuttinginsert 10. In this regard, cutting insert 40 has a base coating layer60, an intermediate coating layer 62, and an outer coating layer 64.

The present invention is further described by the following examplewhich is provided solely for the purpose of description, and is notintended to limit the scope of the invention. Inventive Example No. 1 isset forth in conjunction with Comparative Examples Nos. 1 through 3.

For the inventive and the comparative examples, the substrate powderscontained about 5.8 weight percent cobalt, about 5.2 weight percenttantalum, about 2.0 weight percent titanium, and the balance wastungsten and carbon. The titanium was added in the form of titaniumnitride. The tantalum was added in the form of tantalum carbide. Thetungsten was added as tungsten carbide and tungsten and the carbon wasadded in the form of tungsten metal and carbon black. The mixes werecharged to various levels of carbon as set forth in Table I below.

TABLE I Levels of Charged Carbon in the Examples Comparative ComparativeComparative Inventive Example Example Example Example Example No. 1 No.2 No. 3 No. 1 Charged 5.92 5.98 6.01 5.95 Carbon (wt. %)

The 5 kilograms (kg) of the mix charge for each example was added to a7.5 inch inside diameter by 9 inch steel mill jar along with 21 kg of ⅜inch diameter cemented carbide cycloids and heptane to the top of thejar. The mix was rotated for 40 hours at 52 revolutions per minute (rpm)at ambient temperature. The slurry from each charge was dried, paraffinadded as a fugitive binder, and the powders were granulated so as toprovide for adequate flow properties. The granulated powders werepressed into SNG433 style cutting insert blanks and sintered at 2650° F.(1456° C.) for about 30 minutes under a vacuum. These cutting insertsubstrates were then allowed to furnace cool.

The rake faces were then ground and the cutting insert blanks reheatedat 2650° F. (1456° C.) for about 60 minutes under a vacuum followed by acontrolled cool down of 100° F. (56° C.)/hour until reaching 2100° F.(1149° C.). Table II below presents properties of the resultantsubstrates after reheating.

TABLE II Compositions and Physical Properties of Comparative Examplesand Examples of the Present Invention Comparative ComparativeComparative Inventive Kennametal Property/Example Example No. 1 ExampleNo. 2 Example No. 3 Example No. 1 KC850 Grade Mag. Sat. (gauss- 155 158158 158 158 cm³/g cobalt) H_(c) (oersteds) 146 142 148 149 160 Hardness91.5 91.3 91.4 91.3 91.6 (Rockwell A) Depth of Binder 32 40 42 45 20Enrichment (μm)

The cutting insert blanks were then peripheral ground and honed so thatin the resulting substrate there was cobalt enrichment on the rake facesand the flank faces did not have cobalt enrichment. The cutting insertblanks were then coated with a tri-phase coating according to U.S. Pat.No. 4,035,541. The base layer was titanium carbide applied via CVD to athickness of 4.5 micrometers (μm). The intermediate layer was titaniumcarbonitride applied via CVD to a thickness of 3.5 μm. The top layer wastitanium nitride applied via CVD to a thickness of 3.0 μm.

The turning performance for the comparative examples and the inventiveexample was done according to the following test procedure:

Workpiece Material: AISI 4340 Steel (300 BHN)

Turning conditions:

450 surface feet per minute (sfm) [137.2 surface meters per minute] or550 sfm [167.8 surface meters per minute], feed of 0.020 inch perrevolution (ipr) [0.0508 centimeters per revolution] and 0.1 inch (0.254centimeter) depth of cut (doc)

Coolant: TrimSol Regular (20%)

Insert Style SNG-433 with radius hone (0.003 inches) [0.0076centimeters] edge preparation.

Insert Life Criteria:

Maximum Flank Wear=0.030 inches (0.076 centimeters)

Uniform Flank Wear=0.015 inches (0.038 centimeters)

Chip=0.030 inches (0.076 centimeters)

Crater Wear (depth)=0.004 inches (0.010 centimeters)

Nose Wear=0.030 inches (0.076 centimeters)

Depth of Cut Notching=0.030 inches (0.076 centimeters)

The turning performance of the comparative examples and the inventiveexample was also done according to the following procedure:

Workpiece Material: AISI 1045 Steel (210 BHN)

Turning conditions:

750 sfm (228.8 surface meters per minute) 0.020 ipr (0.0508 centimetersper revolution) 0.1 inch (0.254 centimeter) depth of cut (doc)

Coolant: TrimSol Regular (20%)

Insert Style SNG-433 with radius honed (0.003 inches) [0.0076centimeters] edge preparation.

Insert Life Criteria:

Maximum Flank Wear=0.030 inches (0.076 centimeters)

Uniform Flank Wear=0.015 inches (0.038 centimeters)

Chip=0.030 inches (0.076 centimeters)

Crater Wear (depth)=0.004 inches (0.010 centimeters)

Nose Wear=0.030 inches (0.076 centimeters)

Depth of Cut Notching=0.030 inches (0.076 centimeters)

The impact strength of the comparative examples and the inventiveexample was done according to the following slotted bar (41L50 steel)turning test procedure:

Speed: 350 sfm (106.8 surface meters per minute)

Depth of Cut=0.1 inches (0.254 centimeters)

Feed=the starting feed was 0.015 inches per revolution (0.038centimeters per revolution) with the feed increased 0.005 inches perrevolution (0.0127 centimeters per revolution) every 100 impacts untilthe test reached 800 impacts which was a feed of 0.050 inches perrevolution (0.127 centimeters per revolution) or until breakage,whichever occurred first.

Table III below sets forth the test results for testing of ComparativeExamples Nos. 1 through 4 and the Inventive Example No. 1.

TABLE III Insert Life and Edge Strength Test Results for ComparativeExamples No. 1 Through 3 and the Inventive Example No. 1 Edge Strength1045 Steel 4340 Steel 4340 Steel Example/Property Porosity Rating (# ofImpacts) 750 sfm (minutes) 450 sfm (minutes) 550 sfm (minutes) Comp. Ex.No. 1 CO0 635 13.7 24.1 10.6 Comp. Ex. No. 2 CO3 800 10.7 20.7 9.5 Comp.Ex. No. 3 CO4 800 5.6 17.6 7.1 “Kennametal CO3/CO5 800 5.3 18.75 7.2KC850 ® Coated Cutting Insert Inventive Ex. No. 1 CO2 800 13.1 24.1 10.5

The porosity rating for Table III is done according to the ASTMDesignation B 276-86, entitled “Standard Test Method for ApparentPorosity in Cemented Carbides.” The depth of the binder enrichment wasdetermined by optical examination of a cross-section of the specimen viaa metallograph at a magnification of 1500×.

The edge strength sets forth the number of impacts until either breakageor the test was terminated at 800 impacts via the slotted bar testdescribed above. The turning test results reflect the inserts tool lifein minutes from the test procedures described above.

The data from Table III shows very clearly that the Inventive ExampleNo. 1 has excellent slotted bar edge strength (800 impacts). It alsodemonstrated excellent tool life in the turning of 1045 and 4340 steels.The overall metalcutting properties of the Inventive Example No. 1 aresuperior to all of the other examples shown (i.e., Comparative ExamplesNos. 1 through 3 and the “Kennametal KC850®” coated cutting insert).

More specifically, the edge strength of the Inventive Example No. 1 isequivalent to the edge strength of the higher carbon ComparativeExamples Nos. 2 and 3, and superior to the edge strength of the lowercarbon Comparative Example No. 1. Inventive Example No. 1 also has anedge strength that is equivalent to that of the higher carbon alloy“Kennametal KC850®” coated cutting insert.

Along with the excellent edge strength, the Inventive Example No. 1 alsodemonstrated superior 1045 steel tool life in comparison to the otherhigh carbon examples. Inventive Example No. 1 had a tool life of 13.1minutes in comparison with 10.7 minutes for Comparative Example No. 2,5.6 minutes for Comparative Example No. 3, and 5.3 minutes for the“Kennametal KC850®” coated cutting insert. The 4340 steel tool life ofthe Inventive Example No. 1 is also superior to the tool life of theother (800 impact) edge strength higher carbon examples (e.g.,Comparative Examples Nos. 2 and 3, and the “Kennametal KC850®” coatedcutting insert). Although the 4340 and 1045 steel tool life was onlyequivalent to, or slightly lower than, the lower carbon ComparativeExample No. 1, the Inventive Example No. 1 has superior edge strength inthat it sustained 800 impacts verses 635 impacts for Comparative ExampleNo. 1.

It is very apparent that the present invention presents a cutting insertwith improved characteristics over the Comparative Examples Nos. 1through 3, as well as the “Kennametal KC850®” coated cutting insert.These improved characteristics are especially apparent in conjunctionwith the impact strength and wear resistance demonstrated in theinterrupted and continuous turning of steel as shown above.

All patents and other documents identified in this application arehereby incorporated by reference herein.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as illustrative only, with the true scope andspirit of the invention being indicated by the following claims.

What is claimed is:
 1. A cutting insert comprising: a rake face and aflank face, a cutting edge at the juncture of the rake face and theflank face; the cutting insert having a coating and a substrate whereinthe coating is adherently bonded to the substrate; the substrate being atungsten carbide-based ceramic carbide having a bulk compositioncomprising: the substrate being a tungsten carbide-based cementedcarbide having a bulk composition comprising: at least about 70 weightpercent tungsten carbide, at least about 3 weight percent cobalt, andsolid solution carbides and/or carbonitrides of tungsten and one or moreof one of tantalum, niobium, titanium, hafnium, zirconium, and vanadium;wherein the cobalt concentration being enriched in a zone ofnon-stratified cobalt enrichment beginning near and extending inwardlyfrom a peripheral surface of the substrate, the enriched zone having amaximum cobalt concentration of between about 125 and about 300 percentof the cobalt in the bulk substrate; the zone of non-stratified cobaltenrichment being at least partially depleted of the solid solutioncarbides and/or solid solution carbonitrides; and wherein the bulksubstrate having a porosity according to ASTM Designation B 276-86 ofgreater than C00 and less than or equal to C02.
 2. The cutting insert ofclaim 1 wherein the bulk composition comprises at least about 80 weightpercent tungsten carbide and at least about 5 weight percent cobalt. 3.The cutting insert of claim 1 wherein the bulk composition including upto about 12 weight percent tantalum, up to about 6 weight percentniobium, up to about 10 weight percent titanium, and the balancecomprising tungsten, nitrogen and carbon and cobalt.
 4. The cuttinginsert of claim 3 wherein the sum of the tantalum content and theniobium content is between about 3 weight percent and about 7 weightpercent and the titanium content is between about 0.5 weight percent andabout 5 weight percent.
 5. The cutting insert of claim 1 wherein thesolid solution carbides and/or solid solution carbonitrides are solidsolution carbides and/or carbonitrides of tungsten and one or more ofone of tantalum, niobium, and titanium.
 6. The cutting insert of claim 1wherein the zone of non-stratified cobalt enrichment being whollydepleted of the solid solution carbides and/or solid solutioncarbonitrides.
 7. The cutting insert of claim 1 wherein the enrichedzone has a maximum cobalt content of between about 150 and about 250percent of the cobalt in the bulk substrate.
 8. The cutting insert ofclaim 1 wherein the enriched zone has a maximum cobalt content ofbetween about 200 and about 300 percent of the cobalt in the bulksubstrate.
 9. The cutting insert of claim 1 wherein there is a thinlayer adjacent to the peripheral surface wherein the cobaltconcentration being depleted due to evaporation.
 10. The cutting insertof claim 1 wherein the zone of cobalt enrichment begins at theperipheral surface of the substrate.
 11. The cutting insert of claim 1wherein the zone of cobalt enrichment extends to a depth of up to about50 micrometers from the peripheral surface.
 12. The cutting insert ofclaim 1 wherein the substrate is formed from sintering a consolidatedmass of starting powders.
 13. The cutting insert of claim 1 wherein thecoating comprises: a base layer deposited directly onto the surface ofthe substrate, the base layer having a thickness of between about 3micrometers and about 6 micrometers, and the base layer comprising oneor more materials selected from the group consisting of titaniumcarbide, titanium carbonitride and titanium nitride; an intermediatelayer deposited directly onto the base layer, the intermediate layerhaving a thickness of between about 2 micrometers and about 5micrometers, and the intermediate layer comprising one or more materialsselected from the group consisting of titanium carbonitride, titaniumnitride, titanium carbide, alumina, and titanium aluminum nitride; andan outer layer deposited directly onto the intermediate layer, the outerlayer having a thickness of between about 1.5 micrometers and about 4micrometers, and the outer layer comprising one or more materialsselected from the group consisting of titanium nitride, titaniumcarbonitride, titanium aluminum nitride, and alumina.
 14. The cuttinginsert of claim 1 wherein the bulk substrate having a porosity accordingto ASTM Designation 276-86 of C02.
 15. The cutting insert of claim 1wherein the coating comprising one or more layers wherein the layers areapplied by one or more of physical vapor deposition, conventionalchemical vapor deposition, and moderate temperature chemical vapordeposition.
 16. The cutting insert of claim 1 wherein the zone of cobaltenrichment extends from the rake surface, and there is an absence ofcobalt enrichment extending from the flank surface.